1. Field of the Invention
Embodiments of the present invention generally relate to a reticle, and more particularly, to a reticle including an exposure monitoring key, an exposure apparatus including the reticle, and an exposure method.
2. Description of the Related Art
Recently, as an information-oriented society has developed rapidly, various digital appliances have been developed accordingly. Such digital appliances include components, such as memory/non-memory semiconductor chips and flat panel display apparatuses, which are fabricated by performing micro patterning processes that are beyond simple assembly processes. In particular, it is important to develop a micro patterning technology for forming thin, small, and large-capacity digital appliances. One widely used method of forming fine patterns is a photolithography method using light.
According to the photolithography method, for example, a film to be patterned is formed on a substrate, and photoresist having a photosensitive property is applied on the formed film. Then, light is irradiated to the photoresist by using a reticle on which desired patterns are formed and an exposure apparatus, and patterns are formed on the photoresist by using a chemical reaction and the patterns are then transferred to the film by using the patterned photoresist. In such a photolithography method, one of important processes is an exposure process in which light is irradiated to the photoresist by using a reticle.
An exposure apparatus performs an exposure process mainly by using a stepper method or a scanning method.
The scanning method is an exposure method in which an exposure is performed while a substrate and a reticle move in opposite directions at a constant speed ratio, and accordingly, an entire substrate may be exposed at once.
The stepper method is a step and repeat type, in which a plurality of fields are defined on a substrate, exposure of a field is performed through an exposure region of a projection reduction lens, and then, exposure is performed sequentially with respect to a next field. The stepper method has low productivity since alignment and exposure processes have to be repeated in order to expose a substrate including a plurality of fields. On the other hand, the stepper method has high overlay accuracy since the exposure may be performed once when one alignment key is detected from one entire field. Also, in the stepper method, an intensity of light irradiated onto the substrate may be adjusted only in a state where the substrate and the reticle are stopped, and thus, the exposure may be performed accurately.
When performing the exposure process by using the exposure apparatus, a blind attached to the exposure apparatus blocks some of the light irradiated from a light source to adjust the intensity and shape of the light irradiated to the reticle. However, twisting of a few to thousands of micrometers or hunting may occur due to problems of a driving motor of the blind, degradation of a light shielding blade sensor, bending of the light shielding blade, aging of a timing belt, abnormal operation of an encoder, defects of a driving board, etc. In this case, defective patterns may be formed on the substrate due to misalignment between the blind and the reticle, and therefore, an additional defect detecting process has to be performed in order to sense the defective pattern every time.